I'm trying to render a block from PHP with ServerSideRender as follows:

js file:

/**
 * WordPress dependencies
 */
const { __ } = wp.i18n;
const { registerBlockType } = wp.blocks;
const { ServerSideRender } = wpponents;

/**
 * Internal dependencies
 */
import icons from './../../utils/icons';

registerBlockType( 'name/blockname', {
  title: __( 'blockname' ),
  description: __( 'Lorem Ipsum is simply dummy text of the printing and typesetting industry.' ),
  keywords: [ __( 'recent post' ) ],
  icon: icons.block,
  category: 'xyz',

  edit: ( props ) => {
    const {
      className,
      attributes,
    } = props;

    return (
      <ServerSideRender
        block="name/blockname"
        attributes={ attributes }
        className={ className }
      />
    );
  },

  save: () => {
    return null;
  },
} );

php file:

register_block_type( '.../blockname', array(
   'attributes'      => array(
      'className'    => array(
         'type'      => 'string',
      ),
   ),
   'render_callback' => 'render_block',
) );

function render_block( $attr, $content ) {
    return 'txt';
}

Render:

   <div>txt</div>

Expected:

   <div class="wp-block-name-blockname">txt</div>

Everything seems to work correctly but the div with the class name is not being rendered.

Any suggestion to fix this? thank you in advance.

Anybody have any idea about this?